Delay full sync during yielding Lua scripts to prevent use-after-free (CVE-2026-23631)#3627
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… (CVE-2026-23631) During a full sync, the functions/scripting engine is freed right before loading the RDB from the primary. If a Lua script is still running and yielding via the long-command mechanism at that moment, the freed engine can be accessed when the script resumes, causing a use-after-free. Add a guard at the top of replicaReceiveRDBFromPrimaryToMemory() to check isInsideYieldingLongCommand() and return early, deferring the sync processing until the script completes. No validating test was added because the vulnerability is a race condition between a yielding Lua script and a replication event handler, which cannot be reliably triggered in a deterministic Tcl test. Signed-off-by: ikolomi <ikolomin@amazon.com>
madolson
approved these changes
May 5, 2026
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During a full sync, the functions/scripting engine is freed right before loading the RDB from the primary. If a Lua script is still running and yielding via the long-command mechanism at that moment, the freed engine can be accessed when the script resumes, causing a use-after-free.
Add a guard at the top of replicaReceiveRDBFromPrimaryToMemory() to check isInsideYieldingLongCommand() and return early, deferring the sync processing until the script completes.
No validating test was added because the vulnerability is a race condition between a yielding Lua script and a replication event handler, which cannot be reliably triggered in a deterministic Tcl test.